The present invention is generally directed to the manufacture of a semiconductors device. In particular, the present invention relates to a tool and method for calibrating the dispensing of liquids on a wafer substrate.
The electronics industry continues to rely upon advances in semiconductor technology to realize higher-functioning devices in more compact areas. For many applications, realizing higher-functioning devices requires integrating a large number of electronic devices onto a single silicon wafer. As the number of electronic devices per given area of the silicon wafer increases, the manufacturing process becomes more difficult.
A large variety of semiconductor devices have been manufactured having various applications in numerous disciplines. Such silicon-based semiconductor devices often include metal-oxide-semiconductor (MOS) transistors, such as P-channel MOS (PMOS), N-channel MOS (NMOS) and complementary MOS (CMOS) transistors, bipolar transistors, BiCMOS transistors.
One important step in manufacturing is the formation of devices, or portions thereof, using photolithography and etching processes. In photolithography, a wafer substrate is coated with a light-sensitive material called photo-resist. Next, the wafer is exposed to light; the light striking the wafer is passed through a mask plate. This mask plate defines the desired features to be printed on the substrate. After exposure, the resist-coated wafer substrate is developed. The desired features as defined on the mask are retained on the photoresist-coated substrate. Unexposed areas of resist are washed away with a developer. The wafer having the desired features defined is subjected to etching. Depending upon the production process, the etching may either be a wet etch, in which liquid chemicals are used to remove wafer material or a dry etch, in which wafer material is subjected to a radio frequency (RF) induced plasma.
As device geometry approaches the sub-micron realm, preparation of the wafer for photolithography becomes increasingly important. Integral to successful wafer fabrication, is the consistent and reliable application of photoresist. Improper application of photoresist on the wafer substrate may result in having to rework the wafer at the given process step. Rework results in higher production costs and oftentimes, lower product yield.
Photoresist is often applied to a substrate that is mounted on a chuck in a machine that spins-on the resist. The wafer is loaded on the chuck and held down with vacuum. Through a nozzle, a measured amount of resist is deposited on the wafer. The chuck is rotated at high speed and the centrifugal force on the surface of the wafer spreads the resist across the wafer. A number of parameters determine the characteristics of the applied photoresist.
Conditions that may affect the quality of the photoresist coating may include viscosity of the resist compound, the height and centering of the dispense nozzle with respect to the wafer, hold-down vacuum on the chuck, the speed of the spinner as it is affected by equipment wear. Thus, it behooves the user to monitor the equipment and process for consistency and reliability.
Assuring the uniform dispense of photoresist on the wafer substrate requires that the dispenser nozzle be centered. For example, one technique uses a 200 mm plastic disk marked in even sections having the appearance of a sliced pie. Refer to FIG. 1. Disk 100 is sliced into eight pieces 110. The center point 120 is defined by the intersection of the pieces 110. The disk is placed on the chuck and the nozzle height and centering is adjusted using the disk 100 as a reference. The equipment operator determines the correct height and centering. In an example process, a nozzle height of about 5.5 mm has been found optimal. Depending upon the specific machine, the operator may either center the nozzle manually (by adjusting knobs and other controls) or center the nozzle via software program control of the machine.
This technique is susceptible to operator interpretation and variation. Consequently, there may be lot-to-lot variation in the photo resist application owing to differences in initial equipment setups. Over time, the technique may lack repeatability and consistency.
There exists a need to provide a tool and method of assuring aligned and accurate application of photoresist on the wafer substrate. Consequently, wafer loss from improper photoresist application is minimized, thereby increasing wafer yields and lowering production costs.
The present invention is exemplified in a number of implementations, one of which is summarized below. A calibration tool is used to adjust the height and center of a liquid dispenser nozzle with respect to the wafer chuck. Use of such a tool minimizes the operator-to-operator and machine-to-machine variability of photoresist application on the wafer substrate. In accordance with one embodiment of the present invention, a tool for calibrating a height and center of a dispenser nozzle with respect to a wafer-holding chuck in a spinner apparatus comprises a substrate of a predetermined thickness and predetermined shape having a top surface and a bottom surface. The top surface has a depression of a first depth and cross-section defined substantially about the middle of the top surface. The bottom surface has a depression of a second depth and cross-section defined substantially about the middle of the bottom surface. The top surface depression is coaxial with the bottom surface depression. A further feature of this embodiment is that the first depth and cross-section of the top surface depression corresponds to a depth and cross-section of the dispense nozzle. An additional feature is the second depth and cross-section of the bottom surface depression corresponds to a depth and cross-section of the wafer-holding chuck. A further feature is that a calibration depth is determined by the thickness of the substrate less the sum of the first depth of the top surface depression plus the second depth of the bottom surface depression substantially about the middle of the depressions. Thus after adjustment, the calibration depth corresponds to the height of the dispense nozzle with respect to the wafer chuck.
In another embodiment according to the present invention, a spinner apparatus has dispenser calibration. The calibration comprises a tool for calibrating a height and center of a dispenser nozzle with respect to a wafer-holding chuck in the spinner apparatus. A storage area in the spinner apparatus retains the tool. A substrate holding clamp retrieves the tool from the storage area. A controller activates the substrate-holding clamps for retrieving the tool from the storage area, places the tool on the wafer-holding chuck, and performs calibration of the height and center of the dispenser nozzle. A feature of this embodiment is that the controller may be a computer system whose calibration commands are stored in a computer-readable medium.
In yet another embodiment according to the present invention, a method for calibrating the height and center of a resist-dispenser nozzle in a spinner apparatus comprises placing a calibration tool on the wafer chuck. The calibration tool comprises a substrate of a predetermined thickness and shape having a top surface and a bottom surface. The top surface has a depression of a first depth and cross-section defined therein substantially about the middle of the top surface. The bottom surface has a depression of a second depth and cross-section defined therein substantially about the middle of the bottom surface. The top surface depression is coaxial with the bottom surface depression. The resist-dispenser nozzle is inserted in the depression of the top surface of the tool at a calibration depth defined by the first depth.
The above summaries of the present invention are not intended to represent each disclosed embodiment, or every aspect, of the present invention. Other aspects and example embodiments are provided in the figures and the detailed description that follows.